Common organic electroluminescent devices (OLEDs) comprise a functional layer stack on top of a substrate with at least one organic electroluminescent layer sandwiched between a substrate and a counter electrode, whereas parts of the electroluminescent layer and/or parts of the counter electrode are sensitive to water and/or oxygen. Therefore OLEDs are encapsulated by cover lids to prevent ambient substance such as water and oxygen from reaching the functional layers, to provide OLED devices having a sufficient lifetime. The cover lid defines an encapsulated volume around the functional layer stack with typically a gap or space between the outermost layer of the functional layer stack and the inner side of the cover lid. This gap or space may be filled with inert gas, e.g. dry nitrogen.
A problem of OLEDs encapsulated with a cover lid is the mechanical stability of this encapsulation. Pressure differences in the surrounding environment may give rise to substantially deformations in the cover lid, especially in case of large area OLED devices. The deformations of the cover lid may be so high, that the cover lid touches the functional layer stack of the OLED device causing failures, e.g. shorts, of the OLED device.
Document WO2009001241 discloses an OLED encapsulated with a cover lid comprising shunting structures forming a grid of linear non-transparent metallic stripes to obtain a more homogeneous voltage distribution across the substrate electrode, where each metallic strip extends over the complete lengths of the substrate electrode. Each shunting stripe is completely covered by a smooth non-conductive structure to facilitate the formation of a continuous organic layer and counter electrode layer thereon. The resulting grid of non-conductive structures on top of the shunting structures simultaneously serves as spacer structures preventing electrical shorts between the counter electrode and the substrate electrode as a result of mechanical contact between the lid and the functional layer stack. However, the OLED area covered by the spacer structures and non-transparent shunting structures does not emit light and thus is visible as a disturbing grid of black lines. The presence of black lines prevents a homogeneous brightness distribution over the whole light emitting area of the OLED device.